The invention relates generally to safety and control units for gas hot water heaters and in particular to a gas-fired hot water heater which operates without a permanent burner pilot.
Gas-fired water heaters not employing a permanent burner pilot generally use a control and regulation unit between the main gas control valve and the inlet fitting of the gas burner, as described in French Pat. No. 1336039 assigned to the assignee of this application. This control and regulation device consists of a diaphram pressure regulator arranged so that its closure mechanism for the gas flow is located at two positions on either side of the maximum open position. One position corresponds to the diaphram extended position, the other to the relaxed position of the diaphram. The closure mechanism of the regulator and control mechanism is mechanically secured to a second diaphram. This second diaphram has one face permanently exposed to the pressure of outside air. The other side of the second diaphram communicating with a secondary chamber, can be subjected to the gas pressure upstream of the gas control valve through a valve which is controlled by a thermally sensitive device of low inertia. The thermally sensitive device detects the ignition of a first pilot, the igniter pilot, which will normally operate momentarily when gas is first supplied. The secondary chamber, under the face of the second diaphram, is connected to a second pilot, the safety pilot.
It is also known, through the French Patent of Addition No. 96318, filed by the assignee of this application, that one can use a safety mechanism which has a single valve to control both the gas flow to the burner and to the igniter pilot. In one position of the valve, it shuts off the flow of gas to the burner and opens the flow of gas to the igniter pilot. In its other position, the valve opens the flow of the gas to the burner and shuts off the flow of gas to the igniter pilot. The movement of a sliding stem which supports the particular valve illustrated in this patent is mechanically tied to the motion of a diaphragm which has one face in contact with external air pressure. The other face of the diaphragm can be subjected to the gas pressure upstream of the main control valve for the water heater, through a small valve activated by a thermal device of low inertia operating in response to the igniter pilot.
However, these arrangements have several problems. In the referred to embodiments, the gas valve is opened by the introduction of water within the unit which causes the gas control valve to open through a push rod. The rod in turn raises a contact blade which closes the electrical circuit of the igniter. Thus control of the igniter does not depend upon the level of gas pressure in the line. At the same time, the gas flows to the igniter pilot and lights up when it contacts the igniter. This causes the thermal element of a flame detector, located adjacent the flame of the igniter pilot, to heat up.
If for any reason, the gas pressure is below the distribution pressure normally associated with this type of device, the igniter pilot will light up nevertheless and heat up the thermally sensitive element. As a result, the valve associated with the thermally sensitive element opens and provides gas to the safety pilot which then turns on. However, in this case the gas pressure is insufficient to raise the diaphram, and its associated moving equipment, whose function it is to shut down the igniter pilot, to terminate power to the igniter, and to open the burner gas inlet valve. Consequently, the thermal element is consistently heated by the flame of the ignition pilot, and the ignition circuit is permanently energized. This condition can bring about a rather quick deterioration of these two parts.
An object of the invention is therefore a gas-fired hot water heater having a safety ignition circuit in which the energizing and the de-energizing of the igniter are positively controlled directly by the gas pressure so that continuous operation of the igniter cannot occur.
Other objects of the present invention are a gas-fired water heater having an ignition control device which is reliable and safe.